FIG. 1 shows a fundamental arrangement of a flexible element as a principal element of the piezoelectric relay, and the mode of operation thereof. Referring to FIG. 1, reference numerals 1 and 1' are piezoelectric porcelain plates which are adhered to each other to constitute a flexible member 2 having a bimorph structure. One end of the flexible member 2 is supported as a cantilever by a support portion 3, and the other end thereof has a relay contact 5 through an insulating member 4. The piezoelectric porcelain plates 1 and 1' are respectively polarized in such a manner that electric fields applied to the piezoelectric porcelain plates 1 and 1' oppose to each other when a voltage is applied thereacross through input electrode lead wires 6 and 6'. Therefore, when the piezoelectric porcelain plate 1 (or 1') is straight, the piezoelectric porcelain plate 1' (or 1) is curved. As a result, the flexible member 2 is displaced as indicated by the broken lines.
In general, since flexible elements have a small displacement, two flexible members are used and displaced in opposite directions so as to double the total displacement, as described in U.S. Pat. No. 4,093,883. Furthermore, since a piezoelectric relay is generally turned on or off when input power is applied thereto, a combination of flexible members which are set from OFF to ON and from ON to OFF, respectively, is required for switching a circuit when power is supplied to the piezoelectric relay.
Known piezoelectric relays which provide a switching operation are described in U.S. Pat. No. 2,471,967 and U.S. Pat. No. 2,835,761. In these piezoelectric relays, the stroke of the movable contact is increased utilizing the principle of the "lever". However, the above-mentioned piezoelectric relays have drawbacks in that their structure is complex and pressure acting on the contact is decreased due to the principle of the "lever". Further, piezoelectric relays which do not utilize the principle of the "lever" are described in U.S. Pat. No. 2,166,763 and U.S. Pat. No. 2,182,340. In these relays, however, opposing contacts are fixed, so that a complex mechanism is required to control a small stroke. Further, the stroke must be increased by increasing drive input electric field.